1. Field of the Invention
The present invention relates to a continuously variable transmission (CVT), and more particularly to a CVT that is suitable for mounting in a vehicle such as a straddle-type vehicle.
2. Description of Related Art
A V-belt type CVT is often used in a straddle-type vehicle such as a scooter motorcycle. A V-belt type CVT includes a primary shaft to which output of a power source such as an engine is input, a secondary shaft that extracts output to be transmitted to a driving wheel, and paired primary and secondary sheaves that are respectively disposed on the primary and secondary shafts, and that have variable groove widths. A V-belt is wound around both sheaves, and a groove width adjustment mechanism varies the groove width of each sheave. As a result, the winding diameter of the V-belt around each sheave is adjusted to adjust the speed change ratio between the sheaves in a continuously variable manner.
Normally, the primary and secondary sheaves are each formed by a fixed flange and a moveable flange with a V-groove formed therebetween. The moveable flange can move in the axial direction of the primary or secondary shaft. The groove width adjustment mechanism moves the moveable flange to adjust the speed change ratio in a continuously variable manner.
There is a known V-belt type CVT in which an electric motor is used to move the moveable flange of the primary sheave, thereby adjusting groove width. Movement driving force of the electric motor moves the moveable flange in either a direction that narrows the width of the groove of the primary sheave (a Top side) or a direction that widens the width of the groove of the primary sheave (a Low side), thereby allowing adjustment of the groove width (for example, refer to Japanese Patent No. 3043061). This V-belt type CVT is suitable for use with a straddle-type vehicle (for example, a motorcycle).
A scooter motorcycle provided with a mechanism for electronically controlling a V-belt type automatic CVT automatically changes the speed change ratio of the CVT without requiring the rider to perform any operations (for example, JP-A-62-175228). More specifically, a pre-set program (map) is performed to automatically change the speed change ratio of the CVT based on information such as vehicle speed, engine speed, accelerator opening degree, or the like. Thus, the rider's maneuvering operations are simpler, which has recently led to adoption of automatic CVTs in various vehicle types.
A motorcycle provided with an automatic CVT that performs this kind of electronic control includes a deceleration lever that riders use to input their intentions. Various types of deceleration levers are known. One deceleration lever allows the speed change ratio of the CVT to be manually set in accordance with the position of the deceleration lever (for example, refer to Japanese Patent No. 2950957). Another deceleration lever is provided with a switch that allows down shift to be performed manually by forcibly changing the speed change ratio (for example, refer to JP-A-62-175228). These known devices allow the advantages of the automatic CVT to be exploited while also allowing the intentions of the rider to be used as a basis for continually obtaining a desired speed change ratio. In addition, driving with use of engine brake, and advance down shift can be performed, thereby reducing the problem of unresponsive acceleration.
The inventor has developed a V-belt type CVT that is provided with a control program (a kick down) that down shifts in accordance with a rider's intentions. Use of the V-belt type CVT provided with the kick down in various types of running condition was investigated. Amongst these, it was found that, if kick down is performed when accelerating again after deceleration, there are occasions when unnecessary racing of the engine causes an un-smooth acceleration feeling.